Methods for assisting in beam sweeping, tracking and recovery

ABSTRACT

Certain aspects of the present disclosure provide various appropriate frame structures, sweep sequences, and procedures that may assist in beam sweeping, tracking and recovery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application Ser. No.62/402,897 entitled “METHODS FOR ASSISTING IN BEAM SWEEPING, TRACKINGAND RECOVERY,” which was filed Sep. 30, 2016. The aforementionedapplication is herein incorporated by reference in its entirety.

INTRODUCTION

Aspects of the present disclosure relate generally to wirelesscommunications systems, and more particularly, to supportingbeamforming.

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includeLong Term Evolution (LTE) systems, code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

In some examples, a wireless multiple-access communication system mayinclude a number of base stations, each simultaneously supportingcommunication for multiple communication devices, otherwise known asuser equipment (UEs). In LTE or LTE-A network, a set of one or more basestations may define an e NodeB (eNB). In other examples (e.g., in a nextgeneration or 5G network), a wireless multiple access communicationsystem may include a number of distributed units (DUs) (e.g., edge units(EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs),transmission reception points (TRPs), etc.) in communication with anumber of central units (CUs) (e.g., central nodes (CNs), access nodecontrollers (ANCs), etc.), where a set of one or more distributed units,in communication with a central unit, may define an access node (e.g., anew radio base station (NR BS), a new radio node-B (NR NB), a networknode, 5G NB, gNB, etc.). A base station or DU may communicate with a setof UEs on downlink channels (e.g., for transmissions from a base stationor to a UE) and uplink channels (e.g., for transmissions from a UE to abase station or distributed unit).

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is new radio (NR), for example, 5G radioaccess. NR is a set of enhancements to the LTE mobile standardpromulgated by Third Generation Partnership Project (3GPP). It isdesigned to better support mobile broadband Internet access by improvingspectral efficiency, lowering costs, improving services, making use ofnew spectrum, and better integrating with other open standards usingOFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink(UL) as well as support beamforming, multiple-input multiple-output(MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues toincrease, there exists a need for further improvements in NR technology.Preferably, these improvements should be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

BRIEF SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedcommunications between access points and stations in a wireless network.

Certain aspects of the present disclosure provide a method for wirelesscommunication that may be performed, for example, by a user equipment(UE). The method generally includes determining a sequence over which atleast one of transmit beams of a base station (BS) or receive beams ofthe UE are scanned over different symbols or symbol portions, andparticipating in a beam refinement procedure based on the sequence.

Certain aspects of the present disclosure provide a method for wirelesscommunication that may be performed, for example, by a base station(BS). The method generally includes determining a sequence over which atleast one of transmit beams of the BS or receive beams of a userequipment (UE) are scanned over different symbols or symbol portions,and participating in a beam refinement procedure based on the sequence.

Aspects generally include methods, apparatus, systems, computer readablemediums, and processing systems, as substantially described herein withreference to and as illustrated by the accompanying drawings.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 is a block diagram conceptually illustrating an exampletelecommunications system, in accordance with certain aspects of thepresent disclosure.

FIG. 2 is a block diagram illustrating an example logical architectureof a distributed RAN, in accordance with certain aspects of the presentdisclosure.

FIG. 3 is a diagram illustrating an example physical architecture of adistributed RAN, in accordance with certain aspects of the presentdisclosure.

FIG. 4 is a block diagram conceptually illustrating a design of anexample BS and user equipment (UE), in accordance with certain aspectsof the present disclosure.

FIG. 5 is a diagram showing examples for implementing a communicationprotocol stack, in accordance with certain aspects of the presentdisclosure.

FIG. 6 illustrates an example of a DL-centric subframe, in accordancewith certain aspects of the present disclosure.

FIG. 7 illustrates an example of an UL-centric subframe, in accordancewith certain aspects of the present disclosure.

FIG. 8 illustrates an example of a P1, P2, and P3 procedure, inaccordance with certain aspects of the present disclosure.

FIG. 9a-9d illustrate different beam sweep sequences, in accordance withcertain aspects of the present disclosure.

FIG. 10 illustrates example operations that may be performed by a BS, inaccordance with certain aspects of the present disclosure.

FIG. 11 illustrates example operations that may be performed by a UE, inaccordance with certain aspects of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer readable mediums for operations that may beperformed in new radio (NR) applications (new radio access technology or5G technology).

NR may support various wireless communication services, such as Enhancedmobile broadband (eMBB) targeting wide bandwidth (e.g. 80 MHz beyond),millimeter wave (mmW) targeting high carrier frequency (e.g. 60 GHz),massive MTC (mMTC) targeting non-backward compatible MTC techniques,and/or mission critical targeting ultra reliable low latencycommunications (URLLC). These services may include latency andreliability requirements. These services may also have differenttransmission time intervals (TTI) to meet respective quality of service(QoS) requirements. In addition, these services may co-exist in the samesubframe.

Beam sweeping, tracking and recovery are considered in the NRenhancements of 3GPP. These may be of particular importance for mmWaspects. Aspects of the present disclosure provide various appropriateframe structures, sweep sequences, and procedures that may assist inbeam sweeping, tracking and recovery.

The following description provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in some other examples. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim. The word “exemplary”is used herein to mean “serving as an example, instance, orillustration.” Any aspect described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otheraspects.

The techniques described herein may be used for various wirelesscommunication networks such as LTE, CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). NRis an emerging wireless communications technology under development inconjunction with the 5G Technology Forum (5GTF). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are releases of UMTS that useE-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, while aspects may be describedherein using terminology commonly associated with 3G and/or 4G wirelesstechnologies, aspects of the present disclosure can be applied in othergeneration-based communication systems, such as 5G and later, includingNR technologies.

Example Wireless Communications System

FIG. 1 illustrates an example wireless network 100 in which aspects ofthe present disclosure may be performed. For example, the wirelessnetwork may be a new radio (NR) or 5G network.

According to aspects of the present disclosure, one or more basestations 110 and UEs 120 may communicate using beamforming. Aspects ofthe present disclosure provide various appropriate frame structures,sweep sequences, and procedures that may assist in beam sweeping,tracking and recovery to improve communication using beamforming.

As will be described in more detail herein, a UE may be in a zoneincluding a serving TRP and one or more non-serving TRPs. The servingand non-serving TRPs may be managed by the same ANC (see e.g., ANC 202managing three TRPs 208 in FIG. 2). In certain scenarios, the UE maywake up to perform cell searches to enhance decoding of paging messages.For example, performing a cell search prior to decoding a paging messagemay allow the UE to select a strongest cell (e.g., identified in thecell search).

According to aspects for supporting UL mobility without zone signals, aUE may transmit a first UL chirp signal. The UE may receive a keep alive(KA) signal, in response to the first chirp signal. The KA may bereceived in a first wake period of a discontinuous receive (DRx) cycle.The UE may transmit a second chirp signal using information determinedfrom the KA signal. Thus, the UE may transmit a second chirp signalwithout the use of a DL zone synchronization signals. Advantageously,the UE may use information from the KA signal (and in information from azone signal) to transmit a subsequent chirp signal. For example, the UEmay determine a transmit power (for open loop power control) based onthe KA. According to another example, the UE may decode a power controlfield in the KA and transmit the second chirp signal based, at least inpart on decoded power control information.

UEs 120 may be configured to perform the operations 1100 and othermethods described herein and discussed in more detail below which mayhelp improve DL-based mobility. Base station (BS) 110 may comprise atransmission reception point (TRP), Node B (NB), 5G NB, access point(AP), new radio (NR) BS, etc.). The NR network 100 may include thecentral unit.

As illustrated in FIG. 1, the wireless network 100 may include a numberof BSs 110 and other network entities. A BS may be a station thatcommunicates with UEs. Each BS 110 may provide communication coveragefor a particular geographic area. In 3GPP, the term “cell” can refer toa coverage area of a Node B and/or a Node B subsystem serving thiscoverage area, depending on the context in which the term is used. In NRsystems, the term “cell” and gNB, Node B, 5G NB, AP, NR BS, NR BS, orTRP may be interchangeable. In some examples, a cell may not necessarilybe stationary, and the geographic area of the cell may move according tothe location of a mobile base station. In some examples, the basestations may be interconnected to one another and/or to one or moreother base stations or network nodes (not shown) in the wireless network100 through various types of backhaul interfaces such as a directphysical connection, a virtual network, or the like using any suitabletransport network.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a frequencychannel, etc. Each frequency may support a single RAT in a givengeographic area in order to avoid interference between wireless networksof different RATs. In some cases, NR or 5G RAT networks may be deployed.

A BS may provide communication coverage for a macro cell, a pico cell, afemto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG), UEs for users in the home,etc.). A BS for a macro cell may be referred to as a macro BS. A BS fora pico cell may be referred to as a pico BS. A BS for a femto cell maybe referred to as a femto BS or a home BS. In the example shown in FIG.1, the BSs 110 a, 110 b and 110 c may be macro BSs for the macro cells102 a, 102 b and 102 c, respectively. The BS 110 x may be a pico BS fora pico cell 102 x. The BSs 110 y and 110 z may be femto BS for the femtocells 102 y and 102 z, respectively. A BS may support one or multiple(e.g., three) cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., a BS or a UE) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE or a BS). A relay station may also be a UE thatrelays transmissions for other UEs. In the example shown in FIG. 1, arelay station 110 r may communicate with the BS 110 a and a UE 120 r inorder to facilitate communication between the BS 110 a and the UE 120 r.A relay station may also be referred to as a relay BS, a relay, etc.

The wireless network 100 may be a heterogeneous network that includesBSs of different types, e.g., macro BS, pico BS, femto BS, relays, etc.These different types of BSs may have different transmit power levels,different coverage areas, and different impact on interference in thewireless network 100. For example, macro BS may have a high transmitpower level (e.g., 20 Watts) whereas pico BS, femto BS, and relays mayhave a lower transmit power level (e.g., 1 Watt).

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the BSs may have similar frametiming, and transmissions from different BSs may be approximatelyaligned in time. For asynchronous operation, the BSs may have differentframe timing, and transmissions from different BSs may not be aligned intime. The techniques described herein may be used for both synchronousand asynchronous operation.

A network controller 130 may couple to a set of BSs and providecoordination and control for these BSs. The network controller 130 maycommunicate with the BSs 110 via a backhaul. The BSs 110 may alsocommunicate with one another, e.g., directly or indirectly via wirelessor wireline backhaul.

The UEs 120 (e.g., 120 x, 120 y, etc.) may be dispersed throughout thewireless network 100, and each UE may be stationary or mobile. A UE mayalso be referred to as a mobile station, a terminal, an access terminal,a subscriber unit, a station, a Customer Premises Equipment (CPE), acellular phone, a smart phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, alaptop computer, a cordless phone, a wireless local loop (WLL) station,a tablet, a camera, a gaming device, a netbook, a smartbook, anultrabook, a medical device or medical equipment, a biometricsensor/device, a wearable device such as a smart watch, smart clothing,smart glasses, a smart wrist band, smart jewelry (e.g., a smart ring, asmart bracelet, etc.), an entertainment device (e.g., a music device, avideo device, a satellite radio, etc.), a vehicular component or sensor,a smart meter/sensor, industrial manufacturing equipment, a globalpositioning system device, or any other suitable device that isconfigured to communicate via a wireless or wired medium. Some UEs maybe considered evolved or machine-type communication (MTC) devices orevolved MTC (eMTC) devices. MTC and eMTC UEs include, for example,robots, drones, remote devices, sensors, meters, monitors, locationtags, etc., that may communicate with a BS, another device (e.g., remotedevice), or some other entity. A wireless node may provide, for example,connectivity for or to a network (e.g., a wide area network such asInternet or a cellular network) via a wired or wireless communicationlink. Some UEs may be considered Internet-of-Things (IoT) devices.

In FIG. 1, a solid line with double arrows indicates desiredtransmissions between a UE and a serving BS, which is a BS designated toserve the UE on the downlink and/or uplink. A dashed line with doublearrows indicates interfering transmissions between a UE and a BS.

Certain wireless networks (e.g., LTE) utilize orthogonal frequencydivision multiplexing (OFDM) on the downlink and single-carrierfrequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDMpartition the system bandwidth into multiple (K) orthogonal subcarriers,which are also commonly referred to as tones, bins, etc. Each subcarriermay be modulated with data. In general, modulation symbols are sent inthe frequency domain with OFDM and in the time domain with SC-FDM. Thespacing between adjacent subcarriers may be fixed, and the total numberof subcarriers (K) may be dependent on the system bandwidth. Forexample, the spacing of the subcarriers may be 15 kHz and the minimumresource allocation (called a ‘resource block’) may be 12 subcarriers(or 180 kHz). Consequently, the nominal FFT size may be equal to 128,256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20megahertz (MHz), respectively. The system bandwidth may also bepartitioned into subbands. For example, a subband may cover 1.08 MHz(i.e., 6 resource blocks), and there may be 1, 2, 4, 8 or 16 subbandsfor system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.

While aspects of the examples described herein may be associated withLTE technologies, aspects of the present disclosure may be applicablewith other wireless communications systems, such as NR.

NR may utilize OFDM with a CP on the uplink and downlink and includesupport for half-duplex operation using TDD. A single component carrierbandwidth of 100 MHz may be supported. NR resource blocks may span 12sub-carriers with a sub-carrier bandwidth of 75 kHz over a 0.1 msduration. Each radio frame may consist of 50 subframes with a length of10 ms. Consequently, each subframe may have a length of 0.2 ms. Eachsubframe may indicate a link direction (i.e., DL or UL) for datatransmission and the link direction for each subframe may be dynamicallyswitched. Each subframe may include DL/UL data as well as DL/UL controldata. UL and DL subframes for NR may be as described in more detailbelow with respect to FIGS. 10 and 11. Beamforming may be supported andbeam direction may be dynamically configured. MIMO transmissions withprecoding may also be supported. MIMO configurations in the DL maysupport up to 8 transmit antennas with multi-layer DL transmissions upto 8 streams and up to 2 streams per UE. Multi-layer transmissions withup to 2 streams per UE may be supported. Aggregation of multiple cellsmay be supported with up to 8 serving cells. Alternatively, NR maysupport a different air interface, other than an OFDM-based. NR networksmay include entities such CUs and/or DUs.

In some examples, access to the air interface may be scheduled, whereina scheduling entity (e.g., a base station) allocates resources forcommunication among some or all devices and equipment within its servicearea or cell. Within the present disclosure, as discussed further below,the scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. Base stations arenot the only entities that may function as a scheduling entity. That is,in some examples, a UE may function as a scheduling entity, schedulingresources for one or more subordinate entities (e.g., one or more otherUEs). In this example, the UE is functioning as a scheduling entity, andother UEs utilize resources scheduled by the UE for wirelesscommunication. A UE may function as a scheduling entity in apeer-to-peer (P2P) network, and/or in a mesh network. In a mesh networkexample, UEs may optionally communicate directly with one another inaddition to communicating with the scheduling entity.

Thus, in a wireless communication network with a scheduled access totime-frequency resources and having a cellular configuration, a P2Pconfiguration, and a mesh configuration, a scheduling entity and one ormore subordinate entities may communicate utilizing the scheduledresources.

As noted above, a RAN may include a CU and DUs. A NR BS (e.g., gNB, 5GNode B, Node B, transmission reception point (TRP), access point (AP))may correspond to one or multiple BSs. NR cells can be configured asaccess cell (ACells) or data only cells (DCells). For example, the RAN(e.g., a central unit or distributed unit) can configure the cells.DCells may be cells used for carrier aggregation or dual connectivity,but not used for initial access, cell selection/reselection, orhandover. In some cases DCells may not transmit synchronizationsignals—in some case cases DCells may transmit SS. NR BSs may transmitdownlink signals to UEs indicating the cell type. Based on the cell typeindication, the UE may communicate with the NR BS. For example, the UEmay determine NR BSs to consider for cell selection, access, handover,and/or measurement based on the indicated cell type.

FIG. 2 illustrates an example logical architecture of a distributedradio access network (RAN) 200, which may be implemented in the wirelesscommunication system illustrated in FIG. 1. A 5G access node 206 mayinclude an access node controller (ANC) 202. The ANC may be a centralunit (CU) of the distributed RAN 200. The backhaul interface to the nextgeneration core network (NG-CN) 204 may terminate at the ANC. Thebackhaul interface to neighboring next generation access nodes (NG-ANs)may terminate at the ANC. The ANC may include one or more TRPs 208(which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, orsome other term). As described above, a TRP may be used interchangeablywith “cell.”

The TRPs 208 may be a DU. The TRPs may be connected to one ANC (ANC 202)or more than one ANC (not illustrated). For example, for RAN sharing,radio as a service (RaaS), and service specific AND deployments, the TRPmay be connected to more than one ANC. A TRP may include one or moreantenna ports. The TRPs may be configured to individually (e.g., dynamicselection) or jointly (e.g., joint transmission) serve traffic to a UE.

The local architecture 200 may be used to illustrate fronthauldefinition. The architecture may be defined that support fronthaulingsolutions across different deployment types. For example, thearchitecture may be based on transmit network capabilities (e.g.,bandwidth, latency, and/or jitter).

The architecture may share features and/or components with LTE.According to aspects, the next generation AN (NG-AN) 210 may supportdual connectivity with NR. The NG-AN may share a common fronthaul forLTE and NR.

The architecture may enable cooperation between and among TRPs 208. Forexample, cooperation may be preset within a TRP and/or across TRPs viathe ANC 202. According to aspects, no inter-TRP interface may beneeded/present.

According to aspects, a dynamic configuration of split logical functionsmay be present within the architecture 200. As will be described in moredetail with reference to FIG. 5, the Radio Resource Control (RRC) layer,Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC)layer, Medium Access Control (MAC) layer, and a Physical (PHY) layersmay be adaptably placed at the DU or CU (e.g., TRP or ANC,respectively). According to certain aspects, a BS may include a centralunit (CU) (e.g., ANC 202) and/or one or more distributed units (e.g.,one or more TRPs 208).

FIG. 3 illustrates an example physical architecture of a distributed RAN300, according to aspects of the present disclosure. A centralized corenetwork unit (C-CU) 302 may host core network functions. The C-CU may becentrally deployed. C-CU functionality may be offloaded (e.g., toadvanced wireless services (AWS)), in an effort to handle peak capacity.

A centralized RAN unit (C-RU) 304 may host one or more ANC functions.Optionally, the C-RU may host core network functions locally. The C-RUmay have distributed deployment. The C-RU may be closer to the networkedge.

A DU 306 may host one or more TRPs (edge node (EN), an edge unit (EU), aradio head (RH), a smart radio head (SRH), or the like). The DU may belocated at edges of the network with radio frequency (RF) functionality.

FIG. 4 illustrates example components of the BS 110 and UE 120illustrated in FIG. 1, which may be used to implement aspects of thepresent disclosure. For example, UE 120 and BS 110 may be configured toperform beam sweeping, tracking and recovery using the frame structures,sweep sequences, and procedures described herein (e.g., with referenceto FIGS. 9a-9d ).

As described above, the BS may include a TRP. One or more components ofthe BS 110 and UE 120 may be used to practice aspects of the presentdisclosure. For example, antennas 452, Tx/Rx 222, processors 466, 458,464, and/or controller/processor 480 of the UE 120 and/or antennas 434,processors 460, 420, 438, and/or controller/processor 440 of the BS 110may be used to perform the operations described herein and illustratedwith reference to FIGS. 10-11.

FIG. 4 shows a block diagram of a design of a BS 110 and a UE 120, whichmay be one of the BSs and one of the UEs in FIG. 1. For a restrictedassociation scenario, the base station 110 may be the macro BS 110 c inFIG. 1, and the UE 120 may be the UE 120 y. The base station 110 mayalso be a base station of some other type. The base station 110 may beequipped with antennas 434 a through 434 t, and the UE 120 may beequipped with antennas 452 a through 452 r.

At the base station 110, a transmit processor 420 may receive data froma data source 412 and control information from a controller/processor440. The control information may be for the Physical Broadcast Channel(PBCH), Physical Control Format Indicator Channel (PCFICH), PhysicalHybrid ARQ Indicator Channel (PHICH), Physical Downlink Control Channel(PDCCH), etc. The data may be for the Physical Downlink Shared Channel(PDSCH), etc. The processor 420 may process (e.g., encode and symbolmap) the data and control information to obtain data symbols and controlsymbols, respectively. The processor 420 may also generate referencesymbols, e.g., for a primary synchronization signal (PSS), primarysynchronization signal (SSS), and cell-specific reference signal. Atransmit (TX) multiple-input multiple-output (MIMO) processor 430 mayperform spatial processing (e.g., precoding) on the data symbols, thecontrol symbols, and/or the reference symbols, if applicable, and mayprovide output symbol streams to the modulators (MODs) 432 a through 432t. Each modulator 432 may process a respective output symbol stream(e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator432 may further process (e.g., convert to analog, amplify, filter, andupconvert) the output sample stream to obtain a downlink signal.Downlink signals from modulators 432 a through 432 t may be transmittedvia the antennas 434 a through 434 t, respectively.

At the UE 120, the antennas 452 a through 452 r may receive the downlinksignals from the base station 110 and may provide received signals tothe demodulators (DEMODs) 454 a through 454 r, respectively. Eachdemodulator 454 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 454 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 456 may obtainreceived symbols from all the demodulators 454 a through 454 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 458 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 460, and provide decoded control informationto a controller/processor 480.

On the uplink, at the UE 120, a transmit processor 464 may receive andprocess data (e.g., for the Physical Uplink Shared Channel (PUSCH)) froma data source 462 and control information (e.g., for the Physical UplinkControl Channel (PUCCH) from the controller/processor 480. The transmitprocessor 464 may also generate reference symbols for a referencesignal. The symbols from the transmit processor 464 may be precoded by aTX MIMO processor 466 if applicable, further processed by thedemodulators 454 a through 454 r (e.g., for SC-FDM, etc.), andtransmitted to the base station 110. At the BS 110, the uplink signalsfrom the UE 120 may be received by the antennas 434, processed by themodulators 432, detected by a MIMO detector 436 if applicable, andfurther processed by a receive processor 438 to obtain decoded data andcontrol information sent by the UE 120. The receive processor 438 mayprovide the decoded data to a data sink 439 and the decoded controlinformation to the controller/processor 440.

The controllers/processors 440 and 480 may direct the operation at thebase station 110 and the UE 120, respectively. The processor 440 and/orother processors and modules at the base station 110 may perform ordirect, e.g., the execution of the functional blocks illustrated in FIG.10, and/or other processes for the techniques described herein. Theprocessor 480 and/or other processors and modules at the UE 120 may alsoperform or direct, e.g., the execution of the functional blocksillustrated in FIG. 11, and/or other processes for the techniquesdescribed herein. The memories 442 and 482 may store data and programcodes for the BS 110 and the UE 120, respectively. A scheduler 444 mayschedule UEs for data transmission on the downlink and/or uplink.

FIG. 5 illustrates a diagram 500 showing examples for implementing acommunications protocol stack, according to aspects of the presentdisclosure. The illustrated communications protocol stacks may beimplemented by devices operating in a in a 5G system (e.g., a systemthat supports uplink-based mobility). Diagram 500 illustrates acommunications protocol stack including a Radio Resource Control (RRC)layer 510, a Packet Data Convergence Protocol (PDCP) layer 515, a RadioLink Control (RLC) layer 520, a Medium Access Control (MAC) layer 525,and a Physical (PHY) layer 530. In various examples the layers of aprotocol stack may be implemented as separate modules of software,portions of a processor or ASIC, portions of non-collocated devicesconnected by a communications link, or various combinations thereof.Collocated and non-collocated implementations may be used, for example,in a protocol stack for a network access device (e.g., ANs, CUs, and/orDUs) or a UE.

A first option 505-a shows a split implementation of a protocol stack,in which implementation of the protocol stack is split between acentralized network access device (e.g., an ANC 202 in FIG. 2) anddistributed network access device (e.g., DU 208 in FIG. 2). In the firstoption 505-a, an RRC layer 510 and a PDCP layer 515 may be implementedby the central unit, and an RLC layer 520, a MAC layer 525, and a PHYlayer 530 may be implemented by the DU. In various examples the CU andthe DU may be collocated or non-collocated. The first option 505-a maybe useful in a macro cell, micro cell, or pico cell deployment.

A second option 505-b shows a unified implementation of a protocolstack, in which the protocol stack is implemented in a single networkaccess device (e.g., access node (AN), new radio base station (NR BS), anew radio Node-B (NR NB), a network node (NN), or the like.). In thesecond option, the RRC layer 510, the PDCP layer 515, the RLC layer 520,the MAC layer 525, and the PHY layer 530 may each be implemented by theAN. The second option 505-b may be useful in a femto cell deployment.

Regardless of whether a network access device implements part or all ofa protocol stack, a UE may implement an entire protocol stack (e.g., theRRC layer 510, the PDCP layer 515, the RLC layer 520, the MAC layer 525,and the PHY layer 530).

FIG. 6 is a diagram 600 showing an example of a DL-centric subframe. TheDL-centric subframe may include a control portion 602. The controlportion 602 may exist in the initial or beginning portion of theDL-centric subframe. The control portion 602 may include variousscheduling information and/or control information corresponding tovarious portions of the DL-centric subframe. In some configurations, thecontrol portion 602 may be a physical DL control channel (PDCCH), asindicated in FIG. 6. The DL-centric subframe may also include a DL dataportion 604. The DL data portion 604 may sometimes be referred to as thepayload of the DL-centric subframe. The DL data portion 604 may includethe communication resources utilized to communicate DL data from thescheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE).In some configurations, the DL data portion 604 may be a physical DLshared channel (PDSCH).

The DL-centric subframe may also include a common UL portion 606. Thecommon UL portion 606 may sometimes be referred to as an UL burst, acommon UL burst, and/or various other suitable terms. The common ULportion 606 may include feedback information corresponding to variousother portions of the DL-centric subframe. For example, the common ULportion 606 may include feedback information corresponding to thecontrol portion 602. Non-limiting examples of feedback information mayinclude an ACK signal, a NACK signal, a HARQ indicator, and/or variousother suitable types of information. The common UL portion 606 mayinclude additional or alternative information, such as informationpertaining to random access channel (RACH) procedures, schedulingrequests (SRs), and various other suitable types of information. Asillustrated in FIG. 6, the end of the DL data portion 604 may beseparated in time from the beginning of the common UL portion 606. Thistime separation may sometimes be referred to as a gap, a guard period, aguard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the subordinate entity (e.g., UE)) to UL communication(e.g., transmission by the subordinate entity (e.g., UE)). One ofordinary skill in the art will understand that the foregoing is merelyone example of a DL-centric subframe and alternative structures havingsimilar features may exist without necessarily deviating from theaspects described herein.

FIG. 7 is a diagram 700 showing an example of an UL-centric subframe.The UL-centric subframe may include a control portion 702. The controlportion 702 may exist in the initial or beginning portion of theUL-centric subframe. The control portion 702 in FIG. 7 may be similar tothe control portion described above with reference to FIG. 6. TheUL-centric subframe may also include an UL data portion 704. The UL dataportion 704 may sometimes be referred to as the payload of theUL-centric subframe. The UL portion may refer to the communicationresources utilized to communicate UL data from the subordinate entity(e.g., UE) to the scheduling entity (e.g., UE or BS). In someconfigurations, the control portion 702 may be a physical downlink (DL)control channel (PDCCH).

As illustrated in FIG. 7, the end of the control portion 702 may beseparated in time from the beginning of the UL data portion 704. Thistime separation may sometimes be referred to as a gap, guard period,guard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the scheduling entity) to UL communication (e.g.,transmission by the scheduling entity). The UL-centric subframe may alsoinclude a common UL portion 706. The common UL portion 706 in FIG. 7 maybe similar to the common UL portion 706 described above with referenceto FIG. 7. The common UL portion 706 may additional or alternativeinclude information pertaining to channel quality indicator (CQI),sounding reference signals (SRSs), and various other suitable types ofinformation. One of ordinary skill in the art will understand that theforegoing is merely one example of an UL-centric subframe andalternative structures having similar features may exist withoutnecessarily deviating from the aspects described herein. In one example,a frame may include both UL centric subframes and DL centric subframes.In this example, the ratio of UL centric subframes to DL subframes in aframe may be dynamically adjusted based on the amount of UL data and theamount of DL data that are transmitted. For example, if there is more ULdata, then the ratio of UL centric subframes to DL subframes may beincreased. Conversely, if there is more DL data, then the ratio of ULcentric subframes to DL subframes may be decreased.

In some circumstances, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

A UE may operate in various radio resource configurations, including aconfiguration associated with transmitting pilots using a dedicated setof resources (e.g., a radio resource control (RRC) dedicated state,etc.) or a configuration associated with transmitting pilots using acommon set of resources (e.g., an RRC common state, etc.). Whenoperating in the RRC dedicated state, the UE may select a dedicated setof resources for transmitting a pilot signal to a network. Whenoperating in the RRC common state, the UE may select a common set ofresources for transmitting a pilot signal to the network. In eithercase, a pilot signal transmitted by the UE may be received by one ormore network access devices, such as an AN, or a DU, or portionsthereof. Each receiving network access device may be configured toreceive and measure pilot signals transmitted on the common set ofresources, and also receive and measure pilot signals transmitted ondedicated sets of resources allocated to the UEs for which the networkaccess device is a member of a monitoring set of network access devicesfor the UE. One or more of the receiving network access devices, or a CUto which receiving network access device(s) transmit the measurements ofthe pilot signals, may use the measurements to identify serving cellsfor the UEs, or to initiate a change of serving cell for one or more ofthe UEs.

Example Beam Training Procedures

As noted above, in certain multi-beam systems (e.g., millimeter wave(mmW) cellular systems), beamforming may be needed to overcome highpath-losses. As described herein, beamforming may refer to establishinga link between a BS and UE, wherein both of the devices form a beam(e.g., exciting a certain subset of clusters in the channel). Both theBS and the UE find at least one adequate beam to form a communicationlink. BS-beam and UE-beam form what is known as a beam pair link (BPL).As an example, on the DL, a BS may use a transmit beam and a UE may usea receive beam corresponding to the transmit beam to receive thetransmission. The combination of a transmit beam and correspondingreceive beam may be a BPL.

As a part of beam management, beams which are used by BS and UE have tobe refined from time to time because of changing channel conditions, forexample, due to movement of the UE or other objects, blockages, etc.Additionally, the performance of a BPL may be subject to fading due toDoppler spread. Because of changing channel conditions over time, theBPL may be periodically updated or refined. Accordingly, it may bebeneficial if the BS and the UE monitor beams and new BPLs.

At least one BPL has to be established for network access. As describedabove, new BPLs may be discovered later for different purposes. Thenetwork may decide to use different BPLs for different channels, or forcommunicating with different BSs (TRPS) or as fall-back BPLs in case anexisting BPL fails or gets blocked.

The UE typically monitors the quality of a BPL and the network mayrefine a BPL from time to time.

FIG. 8 illustrates example 800 for BPL discovery and refinement. In5G-NR, the P1, P2, and P3 procedures are used for BPL discovery andrefinement. The network uses a P1 procedure to enable the discovery ofnew BPLs. In the P1 procedure, as illustrated in FIG. 8, the BStransmits different symbols of a reference signal, each beamformed in adifferent spatial direction such that several (most, all) relevantplaces of the cell are reached. Stated otherwise, the BS transmits beamsusing different transmit beams over time in different directions.

For successful reception of at least a symbol of this “P1-signal”, theUE has to find an appropriate receive beam. It searches using availablereceive beams and applying a different UE-beam during each occurrence ofthe periodic P1-signal.

Once the UE has succeeded in receiving a symbol of the P1-signal it hasdiscovered a BPL. The UE may not want to wait until it has found thebest UE receive beam, since this may delay further actions. The UE maymeasure the reference signal received power (RSRP) and report the symbolindex together with the RSRP to the BS. Such a report will typicallycontain the findings of one or more BPLs.

In an example, the UE may determine a received signal having a highRSRP. The UE may not know which beam the BS used to transmit; however,the UE may report to the BS the time at which it observed the signalhaving a high RSRP. The BS may receive this report and may determinewhich BS beam the BS used at the given time.

The BS may then offer P2 and P3 procedures to refine an individual BPL.The P2 procedure refines the BS-beam of a BPL. The BS may transmit a fewsymbols of a reference signal with different BS-beams that are spatiallyclose to the BS-beam of the BPL (the BS performs a sweep usingneighboring beams around the selected beam). In P2, the UE keeps itsbeam constant. Thus, while the UE uses the same beam as in the BPL (asillustrated in P2 procedure in FIG. 8). The BS-beams used for P2 may bedifferent from those for P1 in that they may be spaced closer togetheror they may be more focused. The UE may measure the RSRP for the variousBS-beams and indicate the best one to the BS.

The P3 procedure refines the UE-beam of a BPL (see P3 procedure in FIG.8). While the BS-beam stays constant, the UE scans using differentreceive beams (the UE performs a sweep using neighboring beams). The UEmay measure the RSRP of each beam and identify the best UE-beam.Afterwards, the UE may use the best UE-beam for the BPL and report theRSRP to the BS.

Over time, the BS and UE establish several BPLs. When the BS transmits acertain channel or signal, it lets the UE know which BPL may beinvolved, such that the UE may tune in the direction of the correct UEreceive beam before the signal starts. In this manner, every sample ofthat signal or channel may be received by the UE using the correctreceive beam. In an example, the BS may indicate for a scheduled signal(SRS, CSI-RS) or channel (PDSCH, PDCCH, PUSCH, PUCCH) which BPL isinvolved. In NR, this information is called quasi-collocation (QCL)indication.

Two antenna ports are QCL if properties of the channel over which asymbol on one antenna port is conveyed may be inferred from the channelover which a symbol on the other antenna port is conveyed. QCL supports,at least, beam management functionality, frequency/timing offsetestimation functionality, and RRM management functionality.

The BS may use a BPL which the UE has received in the past. The transmitbeam for the signal to be transmitted and the previously-received signalboth point in a same direction or are QCL. The QCL indication may beneeded by the UE (in advance of the signal to be received) such that theUE may use a correct receive beam for each signal or channel. Some QCLindications may be needed from time to time when the BPL for a signal orchannel changes and some QCL indications are needed for each scheduledinstance. The QCL indication may be transmitted in the downlink controlinformation (DCI) which may be part of the PDCCH channel. Because DCI isneeded to control the information, it may be desirable that the numberof bits needed to indicate the QCL is not too big. The QCL may also betransmitted in a medium access control-control element (MAC-CE) or radioresource control (RRC) message.

According to one example, whenever the UE reports a BS beam that it hasreceived with sufficient RSRP, and the BS decides to use this BPL in thefuture, the BS assigns it a BPL tag. Accordingly, two BPLs havingdifferent BS beams may be associated with different BPL tags. BPLs thatare based on the same BS beams may be associated with the same BPL tag.Thus, according to this example, the tag is a function of the BS beam ofthe BPL.

As noted above, wireless systems, such as millimeter wave (mmW) systems,bring gigabit speeds to cellular networks, due to availability of largeamounts of bandwidth. However, the unique challenges of heavy path-lossfaced by such wireless systems necessitate new techniques such as hybridbeamforming (analog and digital), which are not present in 3G and 4Gsystems. Hybrid beamforming may enhance link budget/signal to noiseratio (SNR) that may be exploited during the RACH process.

In such systems, the enhanced node B (eNB) and the user equipment (UE)may communicate over active beamformed transmission beams. Active beamsmay be considered paired transmission (Tx) and reception (Rx) beamsbetween the eNB and UE that carry data and control channels such asPDSCH, PDCCH, PUSCH, and PUCCH. As noted above, a transmit beam used bya eNB and corresponding receive beam used by a UE for downlinktransmissions may be referred to as a beam pair link (BPL). Similarly, atransmit beam used by a UE and corresponding receive beam used by a eNBfor uplink transmissions may also be referred to as a BPL.

In order for beamforming to function correctly, the eNB may need tomonitor beams using beam measurements performed (e.g., based onreference signals transmitted by the eNB) and feedback generated at theUE. For example, the eNB may monitor active beams using UE-performedmeasurements of signals such as NR-SS, CSI-RS, DMRS-CSS and DMRS-USS.For that, eNB may send measurement request to the UE and maysubsequently transmit one or more reference signals for measurement atthe UE.

Since the direction of a reference signal is unknown to the UE, the UEmay need to evaluate several beams to obtain the best Rx beam for agiven eNB Tx beam. However, if the UE has to “sweep” through all of itsRx beams to perform the measurements (e.g., to determine the best Rxbeam for a given eNB Tx beam), the UE may incur significant delay inmeasurement and battery life impact. Moreover, having to sweep throughall Rx beams is highly resource inefficient. Thus, aspects of thepresent disclosure provide techniques to assist a UE when performingmeasurements of serving and neighbor cells when using Rx beamforming.

Example Methods for Assisting in Beam Sweeping, Tracking and Recovery

As described above, beam training (i.e., beam sweeping, refinement,tracking and recovery) is considered in the NR enhancements of 3GPP.These may be of particular importance for mmW aspects. Aspects of thepresent disclosure provide various appropriate frame structures, sweepsequences, and procedures that may assist in beam sweeping, tracking andrecovery.

Beamforming generally refers to the use of multiple antennas to controlthe direction of a wavefront by appropriately weighting the magnitudeand phase of individual antenna signals (for transmit beamforming).Beamforming may result in enhanced coverage, as each antenna in thearray may make a contribution to the steered signal, an array gain (orbeamforming gain) is achieved. Receive beamforming makes it possible todetermine the direction that the wavefront will arrive (direction ofarrival, or DoA). It may also be possible to suppress selectedinterfering signals by applying a beam pattern null in the direction ofthe interfering signal.

Adaptive beamforming refers to the technique of continually applyingbeamforming to a moving receiver. Aspects of the present disclosure mayhelp improve adaptive beamforming by providing appropriate framestructures, sweep sequences, and procedures that may assist in beamsweeping, tracking and recovery used in adaptive beamforming.

Various beam management procedures may be implemented and supportedwithin one or multiple TRPs.

In some cases, such as in the P1 procedure described above, a UE may beenabled to make measurements on different TRP Tx beams to supportselection of TRP Tx beams/UE Rx beam(s). For beamforming at a TRP, ittypically includes an intra/inter-TRP Tx beam sweep from a set ofdifferent beams. For beamforming at UE, it typically includes a UE Rxbeam sweep from a set of different beams. TRP Tx beam(s) and UE Rxbeam(s) can be determined jointly or sequentially.

In some cases, such as in the P2 procedure described above, a UE may beenabled to make measurements on different TRP Tx beams to possiblychange inter/intra-TRP Tx beam(s). The change may be from a possiblysmaller set of beams for beam refinement than used above in theselection of TRP Tx and/or UE Rx beams.

In some cases, such as in the P3 procedure described above, a UE may beenabled to make measurements on the same TRP Tx beam to change UE Rxbeam in the case UE uses beamforming. It may be desirable to try andimplement a same procedure design for Intra-TRP and inter-TRP beammanagement. However, a UE may not know whether it is intra-TRP or interTRP beam. Procedures P2 and P3 described above may be performed jointlyand/or multiple times to achieve e.g. TRP Tx/UE Rx beam changesimultaneously.

The P3 procedure may or may not have physical layer procedurespecification impact and may support managing multiple Tx/Rx beam pairsfor a UE. In some cases, assistance information from another carrier maybe considered in beam management procedures. One or more of theprocedures may be applied to any frequency band and can be used insingle/multiple beam(s) per TRP.

Aspects of the present disclosure provide structures and techniques thatmay be applied to beam sweeping, tracking and management procedures.

Aspects of the present disclosure describe beam training (i.e., beamsweeping, beam refinement, etc.) procedures that may involve the use ofmultiple beamforming vectors (e.g., broad/narrow directional beams,multi-directional beams, beams designed for interference management,etc.) to scan at both the eNB and UE sides. In examples presentedherein, different beams are scanned from multiple antenna ports at theeNB side with different REs allocated and carrying orthogonal waveformsfor these ports. This may allow the UE to simultaneously evaluatemultiple beams over a single symbol. Multiple RF chain capabilities atthe UE may help speed candidate beam pair evaluation during theseprocedures.

In the case of beam sweeping (P1 procedure) and beam refinement (P2 andP3 procedures), both eNB and UE side sweeping/refinement may beconsidered since significant performance improvement can be realizedwith sweeping/refinement at either end. In particular, an example may beconsidered with the number of beams to be scanned at the eNB side beingNB with the number of beams to be scanned at the UE side being NU withNB≥NU.

Aspects of the present disclosure provide multiple options/types ofsweeping sequences amenable to this asymmetry. While these options aredescribed below, with reference to a sequence of 12 beam sweeps tofacilitate understanding, those skilled in the art will recognize thatgeneralization to sequences other numbers is possible.

Referring first to FIGS. 9a and 9b , one type of beam sweep sequence inwhich multiple candidate beams are evaluated at the eNB and UE sides isillustrated. Both eNB side as well as UE side beam sweeping/refinementare possible with this type of sequence. The example sequences shown inFIGS. 9a and 9b may be especially useful for application during the P1procedure.

In example FIG. 9a , the eNB remains fixed over a single beam over acontiguous set of symbols as the UE cycles through its beams. In theillustrated example, the eNB scans through the same beam over foursymbols (illustrated with the same shade of grey) as the UE beam changesfrom symbol to symbol over the sequence.

On the other hand, in example FIG. 9b , the UE remains fixed over asingle beam over a contiguous set of symbols as the eNB cycles throughits beams. UE scans through the same beam over three symbols as the eNBbeam changes from symbol to symbol over the sequence.

Either of the example sequences in FIG. 9a or 9 b may be useful, forinstance, depending on the beam switching time constraints at the eNBand UE, respectively. Typically, the beam switching constraint may bemore relaxed at the eNB side (relative to the UE side) and, thus, theexample sequence in example FIG. 9b may be more useful in many cases.

FIG. 9c illustrates another type of beam sweep sequence, in which theeNB round-robins through its beams one by one while the UE is beamformedalong a specific beam (e.g., a low gain pseudo-omni beam that has anapproximately flat beam pattern in the beamspace). In the illustratedexample, the eNB scans through 12 different beams (illustrated withshades of grey) as the UE beam remains fixed over the sequence. Thisprocess may be repeated across the same/different UE side beams acrossdifferent subframes for RSRP improvement, subarray scanning, subarraydiversity combining, etc. The example sequence shown in FIG. 9c is alsoamenable for quick eNB beam refinement or beam recovery and, therefore,it may be especially useful for application during the P2 procedure

FIG. 9d illustrates another type of beam sweep sequence, in which theeNB beam is kept fixed as the UE round-robins through all its beams withthe process repeated through different eNB beams across differentsubframes for RSRP improvement, or other purposes. In the illustratedexample, the eNB scans through the same beam (illustrated with the sameshade of grey) as the UE beam changes from symbol to symbol over thesequence This type of sequence may be useful for a quick scan throughdifferent subarrays at the UE side, if necessary. The example sequencesshown in FIG. 9d may be especially useful for application during the P3procedure.

As illustrated by these example shown in FIGS. 9a-9d , different typesof beam sweep sequences for different levels of beam refinement at eNBand UE sides may be considered. To decide on a particular sequence forany given scenario, performance tradeoffs with the different sequencesmay be studied (e.g., with mmW channel models). As described above, insome embodiments, the sweeping sequences are used when both the BS andUE engage in beam training during the same assignment.

In some embodiments, to help speed up the beam pair evaluation, the eNBmay provide signaling to assist the UE in beamformer candidateselection. For example, the eNB can inform the UE which beams it shouldbe expected to scan over the beam sequence, for example, correspondingto specific choices in terms of subarrays, beam types, beams, and thelike. This information may be based on either a prior report such asthose based on an uplink beam sweep, or similar approaches that allowthe eNB to learn about the UE's beam candidate possibilities. Additionalconsideration may also be placed, for example, on appropriate latenciesnecessary for the UE beams to be set up based on eNB signaling.

There are various options for measurements to take and report for beamsweep procedures. In terms of measurements made in the beamsweeping/refinement procedures at the UE side, multiple options can beconsidered. In some cases, reference signal received power (RSRP) orreference signal received quality (RSRQ) measurements across either theentire band or sub-bands may be useful if the UE could feed thisinformation back to the eNB.

In some embodiments, complex-valued signal comparisons (e.g.,ratios/differences) across multiple beam candidates on differentpanels/polarizations may useful in combining beams that point in similardirections across these panels/polarizations (and may be fed back to theeNB). Such combining may effectively improve the energy in rank-1transmissions by coherent combining across panels/polarizations.Additionally, such complex-valued signal comparisons could also assistin multi-directional/coherent beamforming in higher-rank transmissions.

Generalizing the examples described above, the covariance matrix of thepost-beamforming received signal vector across different ports/RF chainsmay be considered and a UE may report (quantized) entries of this matrixto the eNB to assist in beamforming.

Aspects of the present disclosure provide techniques for measuring andfeeding back wideband/sub-band based RSRP, RSRQ, complex-valued signalcomparisons across multiple beam candidates, covariance matrix ofpost-beamforming received signal vector across different ports/RFchains, etc. in response to different beam sweeping/refinementprocedures. Those skilled in the art will recognize that various otherfeedback mechanisms, as well as other measurement reports, may also beimplemented.

For beam recovery, a beam acknowledgment report may be sent by the UE ifan eNB beam sweep is lost due to packet drop. Alternately, it may be thecase that either the eNB/UE side beams are lost either due to suddenblocking of dominant clusters/paths in the channel, UE mobility, etc. Insuch scenarios, quick recovery mechanisms may be implemented, in aneffort to ensure that the link is not lost irrevocably. Beam sweepsequence such as those shown in FIG. 9c may be amenable to suchscenarios.

The use of wider/broader beams in control channels may also be utilizedthat trade off peak beamforming gain for robustness across a largeangular spread thus preventing its loss due to issues such as blockage.Hierarchical beam design in the context of beam recovery may also beimportant. The beam sweep sequences and techniques presented herein maybe amenable to beam recovery.

FIG. 10 illustrates example operations for use by a base station (BS),such as an eNB, in accordance with certain aspects of the presentdisclosure. Operations 1000 begin, at 1002, by determining a sequenceover which at least one of transmit beams of the BS or receive beams ofa user equipment (UE) are scanned over different symbols or symbolportions. At 1004, operations 1000 continue by participating in a beamtraining procedure based on the sequence.

FIG. 11 illustrates example operations for use by a user equipment (UE),in accordance with certain aspects of the present disclosure. Operations1100 begin, at 1102, by determining a sequence over which at least oneof transmit beams of a base station (BS) or receive beams of the UE arescanned over different symbols or symbol portions. At 1104, operations1100 continue by participating in a beam training procedure based on thesequence.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a userterminal 120 (see FIG. 1), a user interface (e.g., keypad, display,mouse, joystick, etc.) may also be connected to the bus. The bus mayalso link various other circuits such as timing sources, peripherals,voltage regulators, power management circuits, and the like, which arewell known in the art, and therefore, will not be described any further.The processor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer-readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For example, instructions for perform the operations describedherein and illustrated in FIGS. 10-12.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A method for wireless communications by a userequipment (UE), comprising: determining a beam sequence over which atleast one of transmit beams of a base station (BS) or receive beams ofthe UE are scanned over different symbols in a symbol portion, whereinthe UE: uses a same pseudo-omni receive beam across the differentsymbols to receive a different transmit beam of the BS in each symbol ofthe different symbols, or uses a different receive beam in each symbolof the different symbols to receive a pseudo-omni transmit beam of theBS; and participating in a beam training procedure based on the beamsequence.
 2. The method of claim 1, further comprising: receivingsignaling from the BS including information related to the beamsequence.
 3. The method of claim 1, further comprising: sending a reportto the BS, based on measurements for different transmit receive beampairs over a certain bandwidth or sub-bands.
 4. The method of claim 3,wherein the report is based on complex-valued signal comparisons acrossmultiple transmit and receive beam pair candidates based on differentpanels or polarizations.
 5. The method of claim 3, wherein the reportincludes at least a portion of a covariance matrix based onpost-beamforming received signal vectors across different ports or radiofrequency (RF) chains.
 6. The method of claim 1, wherein the beamsequence is used for a P2 procedure for refining an existing transmitbeam of the BS in a beam pair link (BPL) established with the UE.
 7. Themethod of claim 1, wherein the beam sequence is used for a P3 procedurefor refining an existing receive beam of the UE in a beam pair link(BPL) established with the BS.
 8. An apparatus for wirelesscommunications, comprising: means for determining a beam sequence overwhich at least one of transmit beams of a base station (BS) or receivebeams of the apparatus are scanned over different symbols in a symbolportion, wherein the apparatus: uses a same pseudo-omni receive beamacross the different symbols to receive a different transmit beam of theBS in each symbol of the different symbols, or uses a different receivebeam in each symbol of the different symbols to receive a pseudo-omnitransmit beam of the BS; and means for participating in a beam trainingprocedure based on the beam sequence.
 9. The apparatus of claim 8,further comprising: means for receiving signaling from the BS includinginformation related to the beam sequence.
 10. A method for wirelesscommunications by a base station (BS), comprising: determining a beamsequence over which at least one of transmit beams of the BS or receivebeams of a user equipment (UE) are scanned over different symbols in asymbol portion wherein the BS: uses a same pseudo-omni transmit beamacross the different symbols to receive a different receive beam of theUE in each symbol of the different symbols, or uses a different transmitbeam in each symbol of the different symbols to receive a pseudo-omnireceive beam of the UE; and participating in a beam training procedurebased on the beam sequence.
 11. The method of claim 10, furthercomprising: transmitting signaling to the UE including informationrelated to the beam sequence.
 12. The method of claim 10, furthercomprising: receiving a report from the UE, wherein the report is basedon measurements for different transmit receive beam pairs over a certainbandwidth or sub-bands.
 13. The method of claim 12, wherein the reportis based on complex-valued signal comparisons across multiple transmitand receive beam pair candidates based on different panels orpolarizations.
 14. The method of claim 12, wherein the report includesat least a portion of a covariance matrix based on post-beamformingreceived signal vectors across different ports or radio frequency (RF)chains.
 15. The method of claim 10, wherein the beam sequence is usedfor a P2 procedure for refining an existing transmit beam of the BS in abeam pair link (BPL) established with the UE.
 16. The method of claim10, wherein the beam sequence is used for a P3 procedure for refining anexisting receive beam of the UE in a beam pair link (BPL) establishedwith the BS.
 17. An apparatus for wireless communications, comprising:means for determining a beam sequence over which at least one oftransmit beams of the apparatus or receive beams of a user equipment(UE) are scanned over different symbols in a symbol portion, wherein theUE: uses a same pseudo-omni transmit beam across the different symbolsto receive a different receive beam of the UE in each symbol of thedifferent symbols, or uses a different transmit beam in each symbol ofthe different symbols to receive a pseudo-omni receive beam of the UE;and means for participating in a beam training procedure based on thebeam sequence.
 18. The apparatus of claim 17, further comprising meansfor transmitting signaling to the UE including information related tothe beam sequence.